Power converter having a switch coupled between windings

ABSTRACT

An example power converter includes a first winding, a second winding, a switch, a controller and an output circuit. The second winding is magnetically coupled to the first winding and the controller includes a feedback terminal and a common terminal. The controller is coupled to control the switch to regulate an output of the power converter in response to a feedback voltage received at the feedback terminal. The output circuit is coupled between the common terminal of the controller and a common reference of the power converter to provide an output voltage to a load. The feedback voltage is a positive voltage with respect to the common terminal and the output voltage is a negative voltage with respect to the common reference of the power converter.

REFERENCE TO PRIOR APPLICATIONS

This application is a continuation-in-part of U.S. Non-Provisionalapplication Ser. No. 12/648,003, filed Dec. 28, 2009, herebyincorporated by reference.

TECHNICAL FIELD

This disclosure relates generally to power converter, and in particularbut not exclusively, relates to ac-dc power converters.

BACKGROUND INFORMATION

Electronic devices use power to operate. Switched mode power suppliesare commonly used due to their high efficiency, small size and lowweight to power many of today's electronics. Conventional wall socketsprovide a high voltage alternating current. In a switching power supplya high voltage alternating current (ac) input is converted to provide awell regulated direct current (dc) output through an energy transferelement. A typical switching power supply also comprises a switchcoupled to the energy transfer element and a power supply controlcircuit coupled to the switch. The switched mode power supply controlcircuit usually regulates an output voltage of the power supply, outputcurrent of the power supply, or a combination of the two by sensing theoutput and controlling it in a closed loop. In operation, the switch isutilized to provide the desired output by varying the duty cycle(typically the ratio of the on-time of the switch to the total switchingperiod) of the switch in a switched mode power supply.

A buck converter is one type of switching power supply where the dutycycle is substantially the ratio of the output voltage of the switchingpower supply to the input voltage when operating in continuous currentmode. As such the ratio of the on-time and the off-time of the switchdetermines the output voltage. For loads which require a small outputvoltage in comparison to the input voltage, the duty cycle of the buckconverter is small and as a result the on-time of the switch is small incomparison to the total switching period. For example, a power supplywith an output voltage of 12 V from a rectified ac input voltage of 375V would require an on-time which is 3.2% of the total switching period.For such cases, a tapped buck converter can provide the same outputvoltage to input voltage ratio as a buck converter but with a largerswitch duty cycle. A larger switch duty cycle is desirable to reducelosses in the switch (typically a MOSFET, bipolar transistor or thelike) that is coupled to the energy transfer element of the power supply

In a typical tapped buck converter configuration one end of an inductoris coupled to the switch, while the other end of the inductor is coupledto the output. A freewheeling diode is then coupled to a tap included inthe inductor. A circuit may also be included in the switching powersupply to provide a feedback signal that is representative of the outputof the switching power supply. This feedback signal may then be used bythe power supply control circuit to control the switching of the switchto regulate the output of the switching power supply. However, since thepower supply output and power supply control circuit are referenced todifferent voltage levels in a tapped buck converter, the feedback signalneeds to be level shifted in order to interface with the controlcircuit. Thus, the typical tapped buck converter configuration mayinclude additional and relatively expensive circuitry for level shiftingthe feedback signal in this way. For example, a conventional tapped buckconverter configuration may include an optocoupler or bias windingcoupled between the output of the switching power supply and the powersupply control circuit to level shift the feedback signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1A is a schematic diagram illustrating a power converter having aswitch in an ON state, in accordance with an embodiment of theinvention.

FIG. 1B is a schematic diagram illustrating the power converter of FIG.1A with the switch in an OFF state.

FIG. 2A is a schematic diagram illustrating a power converter having aswitch in an ON state, in accordance with an embodiment of theinvention.

FIG. 2B is a schematic diagram illustrating the power converter of FIG.2A with the switch in an OFF state.

FIG. 3A is a schematic diagram illustrating a power converter having aswitch in an ON state, in accordance with an embodiment of theinvention.

FIG. 3B is a schematic diagram illustrating the power converter of FIG.3A with the switch in an OFF state.

FIG. 4 is a schematic diagram illustrating a power converter having anintegrated control circuit, in accordance with an embodiment of theinvention.

FIG. 5 is a diagram illustrating a main inductor, in accordance with anembodiment of the invention.

FIG. 6A is a schematic diagram illustrating a power converter having aswitch in an ON state, in accordance with an embodiment of theinvention.

FIG. 6B is a schematic diagram illustrating the power converter of FIG.6A having a switch in an OFF state.

FIG. 7 is a schematic diagram illustrating a power converter withmultiple outputs, in accordance with an embodiment of the invention.

FIG. 8 is a schematic diagram illustrating another power converterhaving multiple outputs, in accordance with an embodiment of theinvention.

FIG. 9 is a schematic diagram illustrating a further power converterhaving multiple outputs, in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION

Embodiments of a power converter having a switch coupled betweenwindings are described herein. In the following description numerousspecific details are set forth to provide a thorough understanding ofthe embodiments. One skilled in the relevant art will recognize,however, that the techniques described herein can be practiced withoutone or more of the specific details, or with other methods, components,materials, etc. In other instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringcertain aspects.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

Throughout this specification, several terms of art are used. Theseterms are to take on their ordinary meaning in the art from which theycome, unless specifically defined herein or the context of their usewould clearly suggest otherwise. A switch that is in an OFF state, alsoreferred to as being an open switch, is a switch that is in a conditionin which the switch does not conduct current. A switch that is in an ONstate, also referred to as being a closed switch, is a switch that is ina condition in which the switch may conduct current.

Embodiments of the present invention include a power converter havingmagnetically coupled windings with a switch coupled between thewindings. Having the switch coupled between the windings allows for thedirect measurement of an output of the power converter for feedbackinformation without the need for additional and expensive level shiftingcomponents typically included in conventional power supply circuits. Oneembodiment of the present invention is a power supply supplying power toLED lamps where the current flowing in the LED lamp needs to beregulated. By positioning the switch and a control circuit coupled todrive the switch between the magnetically coupled windings of an energytransfer element, it is possible to generate a feedback signalrepresentative of the current flowing in the LED lamp without the needto level shift the feedback signal. The feedback signal can therefore bedirectly coupled to the controller to provide a low cost power supplyimplementation. These and other embodiments are described in detailbelow.

FIG. 1A is a schematic diagram illustrating a power converter 100 havinga switch S1 102 in an ON state, in accordance with an embodiment of theinvention. Power converter 100 is illustrated as including switch S1102, a first winding 104, a second winding 106, a core 108, an outputcapacitor C_(O) 110, a diode D1 112, a sense circuit 114, a controller116 and a common reference 118. First winding 104 is illustrated asincluding terminals A and B, while second winding 106 is illustrated asincluding terminals C and D. Switch S1 102 is illustrated as includingterminals 120 and 122. Also shown in FIG. 1A are an input voltage V_(IN)124, an output voltage V_(O) 126, an output current I_(O) 127, a currentI_(ON) 128, a feedback signal 130, a drive signal 132, a reference node134, a node 136, and a load 138.

As shown in FIG. 1A, first winding 104 is magnetically coupled to secondwinding 106 by way of core 108. That is, core 108 is common to bothfirst winding 104 and to second winding 106. In one embodiment, firstwinding 104 and second winding 106 are first and second portions,respectively, of a main inductor. Thus, a main inductor included inpower converter 100 may include a wire wound around a single core, wherethe wire has been separated into first and second portions correspondingto first winding 104 and second winding 106, respectively. In oneembodiment, core 108 includes a ferromagnetic material.

Terminal A of first winding 104 is illustrated as being coupled toreceive input voltage V_(IN) 124. In one embodiment, power converter 100is an ac-dc power converter where input voltage V_(IN) 124 is a dcvoltage that has been generated by rectifying and filtering an ac inputvoltage. Power converter 100 may optionally include rectifier and filtercircuits (not shown) coupled to provide input voltage V_(IN) 124 toterminal A of first winding 104.

Switch S1 102 is illustrated as being coupled between first winding 104and second winding 106. More particularly, FIG. 1A illustrates terminal120 of switch S1 102 as being coupled to terminal B of first winding104, while terminal 122 of switch S1 102 is coupled to reference node134. In one embodiment, switch S1 102 is coupled such that currentI_(ON) 128 flows through first winding 104, through switch S1 102 andthrough second winding 106 when switch S1 is in an ON state (i.e.,closed). Switch S1 102 may be implemented as a semiconductor device suchas for example a metal oxide semiconductor field effect transistor(MOSFET), a bipolar junction transistor (BJT), or an insulated gatebipolar transistor (IGBT).

Controller 116 is coupled to provide drive signal 132 to control switchS1 102 to regulate an output of power converter 100. The regulatedoutput is generally in the form of a regulated voltage (e.g., outputvoltage V_(O) 126), current (e.g., output current I_(O) 127), outputpower or some combination thereof. Controller 116 regulates the outputby controlling switch S1 102 to turn on and off in response to feedbacksignal 130. In the example, feedback signal 130 is representative ofoutput current I_(O) 127. In other examples a feedback signal could berepresentative of output voltage 126, output power or some combinationthereof. Controller 116 may be implemented as a monolithic integratedcircuit, or with discrete electrical components or a combination ofdiscrete and integrated components. Controller 116 and switch S1 102could form part of an integrated control circuit that is manufactured aseither a hybrid or a monolithic integrated circuit.

FIG. 1A further illustrates output capacitor C_(O) 110 as coupledbetween first winding 104 and second winding 106. More particularly, theoutput capacitor C_(O) 110 is coupled to reference node 134 and toterminal C of second winding 106. In the illustrated embodiment, theoutput capacitor C_(O) 110 filters the output of the power converter 100to provide a substantially constant output voltage V_(O) 126 or outputcurrent I_(O) 127. As shown, the output voltage V_(O) 126 is the voltageacross output capacitor C_(O) 110.

Second winding 106 is illustrated in FIG. 1A as being coupled betweenoutput capacitor C_(O) 110 and common reference 118. More particularly,terminal C of second winding 106 is coupled to output capacitor C_(O)110 while terminal D is coupled to common reference 118. As mentionedabove in one embodiment, a current (i.e., current I_(ON) 128) flowsthrough second winding 106, which is substantially the same as thecurrent that flows through first winding 104 and switch S1 102 whenswitch S1 102 is in the ON state.

Diode D1 112 is illustrated as being coupled between reference node 134and common reference 118. More particularly, an anode of diode D1 112may be coupled to common reference 118, while a cathode of diode D1 112is coupled to reference node 134 to provide a path for the current fromsecond winding 106 when switch S1 102 is in the OFF state. For example,FIG. 1B is a schematic diagram illustrating power converter 100 of FIG.1A when switch S1 102 in the OFF state. As shown in FIG. 1B, duringoperation, controller 116 switches switch S1 102 to the OFF state,thereby substantially preventing current from flowing through firstwinding 104 and through switch S1 102. However, as illustrated in FIG.1B, a current (i.e., current I_(OFF) 140) flows through second winding106, which is substantially the same as the current that flows throughdiode D1 112 when switch S1 102 is in the OFF state.

Referring now to both FIGS. 1A and 1B, power converter 100 may include asense circuit 114 coupled to provide feedback signal 130 to controller116. The feedback signal 130 may be a voltage signal or a currentsignal. While FIGS. 1A and 1B illustrate sense circuit 114 as includinga sense resistor R_(SENSE), sense circuit 114 may include discrete,active or a combination of discrete and active components in accordancewith the teachings of the present invention. In one embodiment senseresistor R_(SENSE) is coupled to load 138. That is, sense resistorR_(SENSE) may be coupled to load 138 without isolation circuitrytherebetween. As shown in FIGS. 1A and 1B, sense circuit 114 is furthercoupled between switch S1 102 and controller 116 to provide the feedbacksignal 130, which in one example is representative of output currentI_(O) 127. More particularly, sense circuit 114 is coupled betweenreference node 134 and node 136. In one embodiment, sense circuit 114generates feedback signal 130 in response to a voltage taken withrespect to reference node 134. However, reference node 134 may bedirectly connected (i.e., electrically shorted) to terminal 122 ofswitch S1 102. Thus, sense circuit 114 may generate feedback signal 130in response to a voltage taken with respect to terminal 122 of switch S1102. Sense circuit 114 may also, in one embodiment, generate feedbacksignal 130 in response to a voltage across sense resistor R_(SENSE). Inone example reference node 134 is connected to a common terminal COM ofcontroller 116 by way of optional connection 142 as the reference groundof the controller 116. In one example the reference ground (e.g., commonterminal COM) of the controller 116 is the reference voltage levelrelative to which drive signal 132 is generated and feedback signal 130is sensed. Therefore, embodiments of the present invention may includethe feedback signal 130 generated across sense circuit 114 also relativeto reference node 134.

In one embodiment, controller 116 includes a feedback terminal FB thatis coupled to node 136. When the feedback signal 130 is a voltagesignal, the feedback signal 130 received at the feedback terminal is anegative voltage with respect to terminal 122 of switch S1 102. Thesense circuit 114 provides the feedback signal 130 which isrepresentative of the output current I_(O) 127, output voltage V_(O)126, or a combination of the two. For the embodiment shown in FIGS. 1Aand 1B, the feedback signal 130 provides information regarding theoutput current I_(O) 127 of the power converter 100 during both the ONstate and the OFF state of switch S1 102.

FIG. 2A is a schematic diagram illustrating a power converter 200 havinga switch S1 202 in an ON state, in accordance with an embodiment of thepresent invention. Power converter 200 is illustrated as includingswitch S1 202, a first winding 204, a second winding 206, a core 208, anoutput capacitor C_(O) 210, a diode D1 212, a sense circuit 214, acontroller 216 and a common reference 218. First winding 204 isillustrated as including terminals A and B, while second winding 206 isillustrated as including terminals C and D. Switch S1 202 is illustratedas including terminals 220 and 222. Also shown in FIG. 2A are an inputvoltage V_(IN) 224, an output voltage V_(O) 226, an output current I_(O)227, a current I_(ON) 228, a feedback signal 230, a drive signal 232, areference node 234, a node 236, and a load 238.

As shown in FIG. 2A, first winding 204 is magnetically coupled to secondwinding 206 by way of core 208. That is, core 208 is common to bothfirst winding 204 and to second winding 206. In one embodiment, firstwinding 204 and second winding 206 are first and second portions,respectively, of a main inductor. Thus, a main inductor included inpower converter 200 may include a wire wound around a single core, wherethe wire has been separated into first and second portions correspondingto first winding 204 and second winding 206, respectively. In oneembodiment, core 208 includes a ferromagnetic material.

Terminal A of first winding 204 is illustrated as being coupled toreceive input voltage V_(IN) 224. In one embodiment, input voltageV_(IN) 224 is a rectified and filtered ac voltage. Power converter 200may optionally include rectifier and filter circuits (not shown) coupledto provide input voltage V_(IN) 224 to terminal A of first winding 204.

Switch S1 202 is illustrated as being coupled between first winding 204and second winding 206. FIG. 2A illustrates terminal 220 of switch S1202 as being coupled to terminal B of first winding 204, while terminal222 of switch S1 204 is coupled to reference node 234. In oneembodiment, switch S1 202 is coupled such that current I_(ON) 228 flowsthrough first winding 204, through switch S1 202 and through secondwinding 206 when the switch S1 202 is in an ON state (i.e., closed).Switch S1 202 may be implemented as a semiconductor device such as ametal oxide semiconductor field effect transistor (MOSFET), a bipolarjunction transistor (BJT), or an insulated gate bipolar transistor(IGBT).

Controller 216 is shown in FIG. 2A as being coupled to provide drivesignal 232 to control the switching of the switch S1 202 to regulate anoutput of power converter 200. The regulated output is generally in theform of regulated voltage (e.g., output voltage V_(O) 226), current(e.g., output current I_(O) 227), output power or some combinationthereof. Controller 216 regulates the output by controlling switch S1202 to turn on and off in response to feedback signal 230. Feedbacksignal 230 may be representative of output voltage V_(O) 226, outputcurrent I_(O) 227, output power or some combination thereof. Controller216 may be implemented as a monolithic integrated circuit, may beimplemented with discrete electrical components or may be implemented asa combination of discrete and integrated components. Controller 216 andswitch 51 202 could form part of an integrated control circuit that ismanufactured as either a hybrid or a monolithic integrated circuit.

Second winding 206 is illustrated in FIG. 2A as being coupled betweensense circuit 214 and output capacitor C_(O) 210. FIG. 2A illustratesterminal C of second winding 206 as being coupled to sense circuit 214while terminal D is coupled to output capacitor C_(O) 210. As mentionedabove, a current (i.e., current I_(ON) 228) flows through the secondwinding 206 which is substantially the same as the current that flowsthrough first winding 204 and switch S1 202 when switch S1 202 is in theON state.

FIG. 2A further illustrates output capacitor C_(O) 210 as coupledbetween second winding 206 and common reference 218. In the illustratedembodiment, the output capacitor C_(O) 210 filters the output of thepower converter 200 to provide a substantially constant output voltageV_(O) 226 or output current I_(O) 227. As shown, the output voltageV_(O) 226 is the voltage across output capacitor C_(O) 210

Diode D1 212 is illustrated as being coupled between reference node 234and common reference 218. More particularly, an anode of diode D1 212may be coupled to common reference 218, while a cathode of diode D1 212is coupled to reference node 234 to provide a path for current to flowfrom the second winding 206 when switch S1 202 is in the OFF state. Forexample, FIG. 2B is a schematic diagram illustrating power converter 200of FIG. 2A with switch S1 202 in the OFF state. As shown in FIG. 2B,during operation, controller 216 switches switch S1 202 to the OFFstate, thereby substantially preventing current from flowing throughfirst winding 204 and through switch S1 202. However, as illustrated inFIG. 2B, a current (i.e., current I_(OFF) 240) flows through secondwinding 206, which is substantially the same as the current that flowsthrough diode D1 212 when switch S1 202 is in the OFF state.

Referring now to both FIGS. 2A and 2B, power converter 200 may include asense circuit 214 coupled to provide feedback signal 230 to controller216. Although FIGS. 2A and 2B illustrate sense circuit 214 as includinga sense resistor R_(SENSE), sense circuit 214 may include discrete,active or a combination of discrete and active components in accordancewith the teachings of the present invention. In one embodiment senseresistor R_(SENSE) includes one terminal coupled to reference node 234and another terminal coupled to terminal C of second winding 206. Asshown in FIGS. 2A and 2B, sense circuit 214 is further coupled betweenswitch S1 202 and controller 216 to provide the feedback signal 230,which in one example is representative of output current I_(O) 227. Inone embodiment, sense circuit 214 generates feedback signal 230 inresponse to a voltage taken with respect to reference node 234. However,reference node 234 may be directly connected (i.e., electricallyshorted) to terminal 222 of switch S1 202. Thus, sense circuit 214 maygenerate feedback signal 230 in response to a voltage taken with respectto terminal 222 of switch S1 202. Sense circuit 214 may also, in oneembodiment, generate feedback signal 230 in response to a voltage acrosssense resistor R_(SENSE). In one example reference node 234 is connectedto a common terminal COM of controller 216 by way of optional connection242 as the reference ground of the controller 216. In one example thereference ground (e.g., common terminal COM) of the controller 216 isthe reference voltage level relative to which drive signal 232 isgenerated and feedback signal 230 is sensed. Therefore, embodiments ofthe present invention may include the feedback signal 230 generatedacross sense circuit 214 also relative to reference node 234.

In one embodiment, controller 216 includes a feedback terminal FB whichis coupled to node 236 and thus feedback signal 230 has a negativevoltage with respect to terminal 222 of switch S1 202 and node 234.Furthermore, in the illustrated embodiment of FIGS. 2A and 2B, sensecircuit 214 provides feedback signal 230 which is representative of theoutput of power converter 200 during both the ON state and the OFF stateof switch S1 202.

FIG. 3A is a schematic diagram illustrating a power converter 300 havinga switch S1 302 in an ON state, in accordance with an embodiment of theinvention. Power converter 300 is illustrated as including switch S1302, a first winding 304, a second winding 306, a core 308, an outputcapacitor C_(O) 310, a diode D1 312, a sense circuit 314, a controller316 and a common reference 318. First winding 304 is illustrated asincluding terminals A and B, while second winding 306 is illustrated asincluding terminals C and D. Switch S1 302 is illustrated as includingterminals 320 and 322 and sense circuit 314 is illustrated as includinga resistor R_(SENSE) 340 and a capacitor C_(SENSE) 342. Also shown inFIG. 3A are an input voltage V_(IN) 324, an output voltage V_(o) 326, anoutput current I_(O) 327, a current I_(ON) 328, a feedback signal 330, adrive signal 332, a reference node 334, a node 336, and a load 338.

As shown in FIG. 3A, first winding 304 is magnetically coupled to secondwinding 306 by way of core 308. That is, core 308 is common to bothfirst winding 304 and to second winding 306. In one embodiment, firstwinding 304 and second winding 306 are first and second portions,respectively, of a main inductor. Thus, a main inductor included inpower converter 300 may include a wire wound around a single core, wherethe wire has been separated into first and second portions correspondingto first winding 304 and second winding 306, respectively. In oneembodiment, core 308 includes a ferromagnetic material.

Terminal A of first winding 304 is coupled to receive input voltageV_(IN) 324. In one embodiment, the input voltage V_(IN) 324 is arectified and filtered ac voltage. Power converter 300 may optionallyinclude rectifier and filter circuits (not shown) coupled to provideinput voltage V_(IN) 324 to terminal A of first winding 304.

Switch S1 302 is coupled between first winding 304 and second winding306. More particularly, FIG. 3A illustrates terminal 320 of switch S1302 as being coupled to terminal B of first winding 304, while terminal322 of switch S1 304 is coupled to reference node 334. In oneembodiment, switch S1 302 is coupled such that current I_(ON) 328 flowsthrough first winding 304, through switch S1 302 and through secondwinding 306 when switch S1 302 is in an ON state (i.e., closed). SwitchS1 302 may be implemented as a semiconductor device such as for examplea metal oxide semiconductor field effect transistor (MOSFET), a bipolarjunction transistor (BJT), or an insulated gate bipolar transistor(IGBT).

Controller 316 is shown in FIG. 3A as being coupled to provide drivesignal 332 to control the switching of the switch S1 302 to regulate anoutput of power converter 300. The regulated output is generally in theform of regulated voltage (e.g., output voltage V_(O) 326), current(e.g., output current I_(O) 327), output power or some combinationthereof. Controller 316 regulates the output by controlling switch S1302 to turn on and off in response to feedback signal 330. Feedbacksignal 330 may be representative of output voltage V_(O) 326, outputcurrent I_(O) 327, output power or some combination thereof. Inaddition, the feedback signal 330 may be a voltage signal or a currentsignal. Controller 316 may be implemented as a monolithic integratedcircuit, may be implemented with discrete electrical components or maybe implemented as a combination of discrete and integrated components.Controller 316 and switch S1 302 could form part of an integratedcontrol circuit that is manufactured as either a hybrid or a monolithicintegrated circuit.

Second winding 306 is illustrated in FIG. 3A as being coupled betweenswitch S1 302 and output capacitor C_(O) 310. More particularly, FIG. 3Aillustrates terminal C of second winding 306 as being coupled toreference node 334 while terminal D is coupled to output capacitor C_(O)310. As mentioned above in one embodiment, a current (i.e., currentI_(ON) 328) flows through second winding 306, which is substantially thesame as the current that flows through first winding 304 and switch S1302 when switch S1 302 is in the ON state.

FIG. 3A further illustrates output capacitor C_(O) 310 as coupledbetween second winding 306 and common reference 318. In the illustratedembodiment, the output capacitor C_(O) 310 filters the output voltageV_(O) 326 or the output current I_(O) 327. As shown, the output voltageV_(O) 326 is the voltage across output capacitor C_(O) 310.

Diode D1 312 is illustrated as being coupled between controller 316 andcommon reference 318. More particularly, an anode of diode D1 312 may becoupled to common reference 318, while a cathode of diode D1 312 iscoupled to node 336 to provide a path for current to flow from thesecond winding 306 when switch 51 302 is in the OFF state. For example,FIG. 3B is a schematic diagram illustrating power converter 300 of FIG.3A with switch S1 302 in the OFF state. As shown in FIG. 3B, duringoperation, controller 316 switches switch S1 302 to the OFF state,thereby substantially preventing current from flowing through firstwinding 304 and through switch S1 302. However, as illustrated in FIG.3B, a current (i.e., current I_(OFF) 340) flows through second winding306, which is substantially the same as the current that flows throughdiode D1 312 when switch S1 302 is in the OFF state.

Referring now to both FIGS. 3A and 3B, power converter 300 may include asense circuit 314 coupled to provide feedback signal 330 to controller316. Although FIGS. 3A and 3B illustrate sense circuit 314 as includinga sense resistor R_(SENSE) 340 and a sense capacitor C_(S) 342, sensecircuit 214 may include discrete, active or a combination of discreteand active components in accordance with the teachings of the presentinvention. In one embodiment sense resistor R_(SENSE) 340 includes oneterminal coupled to reference node 334 and another terminal coupled tonode 336 with sense capacitor C_(S) 342 coupled across sense resistorR_(SENSE) 340. As shown in FIGS. 3A and 3B, sense circuit 314 is furthercoupled between switch S1 302 and controller 316 to provide feedbacksignal 330, which in one example is representative of output currentI_(O) 327. In one embodiment, sense circuit 314 generates the feedbacksignal 330 in response to a voltage taken with respect to reference node334. However, reference node 334 may be directly connected (i.e.,electrically shorted) to terminal 322 of switch S1 302. Thus, sensecircuit 314 may generate feedback signal 330 in response to a voltagetaken with respect to terminal 322 of switch S1 302. Sense circuit 314may also generate feedback signal 330 in response to the voltage acrosssense resistor R_(SENSE) 340. In one example reference node 334 isconnected to a common terminal COM of controller 316 by way of optionalconnection 342 as the reference ground of the controller 316. In oneexample the reference ground (e.g., common terminal COM) of thecontroller 316 is the reference voltage level relative to which drivesignal 332 is generated and feedback signal 330 is sensed. Therefore,embodiments of the present invention may include the feedback signal 330generated across sense circuit 314 also relative to reference node 334.

In one embodiment, controller 316 includes a feedback terminal FB thatis directly connected to node 336 and thus feedback signal 330 has apositive voltage with respect to the node 334 and terminal 322 of switchS1 302. Furthermore, in the illustrated embodiment of FIGS. 3A and 3B,sense circuit 314 provides feedback signal 330 which is representativeof an output of power converter 300 during the OFF state of switch S1302. In the example, capacitor C_(S) 342 is therefore placed in parallelto resistor 340 as a means of filtering the voltage signal generatedacross resistor 340 to provide a substantially dc feedback signal 330 tocontroller 316 relative to reference node 334 in accordance with theteachings of the present invention.

FIG. 4 is a schematic diagram illustrating a power converter 400 havingan integrated control circuit 401, in accordance with an embodiment ofthe invention. Power converter 400 is one possible implementation ofpower converter 300 of FIGS. 3A and 3B. Power converter 400 isillustrated as including integrated control circuit 401, a first winding404, a second winding 406, a core 408, an output capacitor C_(O) 410, adiode 412, a sense circuit 414 and a common reference 418. Integratedcontrol circuit 401 is illustrated as including a switch S1 402, acontroller 416, and terminals 403, 405, and 407. First winding 404 isillustrated as including terminals A and B, while second winding 406 isillustrated as including terminals C and D. Sense circuit 414 isillustrated as including a resistor R_(SENSE) 440 and a capacitorC_(SENSE) 442. Also shown in FIG. 4 are an input voltage V_(IN) 424, anoutput voltage V_(O) 426, an output current I_(O) 427, a reference node434, a node 436, and a load 438. Load 438 is illustrated as including anarray of light emitting diodes (LEDs) 444.

As shown in FIG. 4, first winding 404 is magnetically coupled to secondwinding 406 by way of core 408. That is, core 408 is common to bothfirst winding 404 and to second winding 406. In one embodiment, firstwinding 404 and second winding 406 are first and second portions,respectively, of a main inductor. Thus, a main inductor included inpower converter 400 may include a wire wound around a single core, wherethe wire has been separated into first and second portions correspondingto first winding 404 and second winding 406, respectively. In oneembodiment, core 408 includes a ferromagnetic material.

Terminal A of first winding 404 is illustrated as being coupled toreceive input voltage V_(IN) 424. In one embodiment, the input voltageV_(IN) 424 is a rectified and filtered ac voltage. Power converter 400may optionally include rectifier and filter circuits (not shown) coupledto provide input voltage V_(IN) 424 to terminal A of first winding 404.

Integrated control circuit 401 is illustrated as being coupled betweenfirst winding 304 and second winding 306. More particularly, FIG. 4illustrates terminal 403 of integrated control circuit 401 as beingcoupled to terminal B of first winding 404, while terminal 405 ofintegrated control circuit 401 is coupled to reference node 434. In oneembodiment, integrated control circuit 401 is coupled such that currentI_(ON) 428 flows through first winding 404, between terminals 403 and405, and through second winding 406 when switch 402 is in an ON state(i.e., closed). Although FIG. 4 illustrates switch 402 a metal oxidesemiconductor field effect transistor (MOSFET), switch 403 may also beimplemented as a semiconductor device such as for example a bipolarjunction transistor (BJT), or an insulated gate bipolar transistor(IGBT). Switch 402 is illustrated as including a drain terminal coupledto terminal 403 of integrated control circuit 401 and as including asource terminal coupled to terminal 405.

Also included in integrated control circuit 401 is controller 416 whichis coupled to control switching of the switch 402 to regulate the outputcurrent J_(O) 427 of power converter 400. Controller 416 regulates theoutput current J_(O) 427 delivered to load 438 by controlling switch S1402 to turn on and off by generating a drive signal in response to afeedback signal received at feedback terminal 407. The feedback signalat terminal 407 may be representative of the output current J_(O) 427.

Second winding 406 is illustrated in FIG. 4A as being coupled betweenintegrated control circuit 401 and output capacitor C_(O) 410. FIG. 4illustrates terminal C of second winding 406 as being coupled toreference node 434 while terminal D is coupled to output capacitor C_(O)410. As mentioned above in one embodiment, a current (i.e., currentI_(ON) 428) flows through second winding 406, which is substantially thesame as the current that flows through first winding 404 and betweenterminals 403 and 405 of integrated control circuit 401 when switch 402is in the ON state.

FIG. 4 further illustrates output capacitor C_(O) 410 as coupled betweensecond winding 406 and common reference 418. In the illustratedembodiment, the output capacitor C_(O) 410 filters the output of thepower converter 400 to provide a substantially constant output voltageV_(O) 426 or output current J_(O) 427. As shown, the output voltageV_(O) 426 is the voltage across output capacitor C_(O) 410

Diode D1 412 is illustrated as being coupled between integrated controlcircuit 401 and common reference 418. More particularly, an anode ofdiode D1 412 may be coupled to common reference 418, while a cathode ofdiode D1 412 is coupled to node 436 to provide a path for current toflow from second winding 406 when switch 402 is in the OFF state. Duringoperation, controller 416 switches switch 402 to the OFF state, therebysubstantially preventing current from flowing through first winding 404and through switch 402. However, a current (see e.g., current I_(OFF)340 of FIG. 3B) flows through second winding 406, which is substantiallythe same as the current that flows through diode D1 412 when switch 402is in the OFF state.

Power converter 400 may include a sense circuit 414 coupled to provide afeedback signal to feedback terminal 407 of integrated control circuit401. Although FIG. 4 illustrates sense circuit 414 as including a senseresistor R_(SENSE) 440 and a sense capacitor C_(S) 442, sense circuit414 may include discrete, active or a combination of discrete and activecomponents in accordance with the teachings of the present invention. Inone embodiment sense resistor R_(SENSE) 440 includes one terminalcoupled to reference node 434 and another terminal coupled to node 436with sense capacitor C_(S) 442 coupled across sense resistor R_(SENSE).As shown in FIG. 4, sense circuit 414 is further coupled betweenterminals 405 and 407 of integrated control circuit 401. In oneembodiment, sense circuit 414 generates a feedback signal in response toa voltage taken with respect to reference node 434. However, referencenode 434 may be directly connected (i.e., electrically shorted) toterminal 405 of integrated control circuit 401. Thus, sense circuit 414may generate the feedback signal in response to a voltage taken withrespect to terminal 405 of integrated control circuit 401 where in oneexample terminal 405 is a common terminal (e.g., the reference ground ofintegrated control circuit 401). In one example the reference ground(e.g., common terminal 405) of integrated control circuit 401 is thereference voltage level relative to which a drive signal is generated bycontroller 416 and then applied to the gate of switch 402. Thus, thereference ground of both controller 416 and of integrated controlcircuit 401 may be the reference voltage level at common terminal 405.Also, the reference ground of integrated control circuit 401 may be thereference voltage level relative to which a feedback signal that isreceived at feedback terminal FB 407 is sensed. Therefore, embodimentsof the present invention may include a feedback signal received atfeedback terminal FB 407 that is generated across sense circuit 414 alsorelative to common terminal 405.

Sense circuit 414 may also generate the feedback signal in response to avoltage across sense resistor R_(SENSE). In the illustrated embodiment,the voltage across sense resistor R_(SENSE) 440 is representative ofoutput current I_(O) 427 when switch 402 is in the OFF state andcapacitor C_(S) 442 filters the voltage across sense resistor R_(SENSE)440 to provide a substantially dc feedback signal to FB terminal 407 ofintegrated circuit 401.

In the illustrated embodiment, feedback terminal 407 is directlyconnected to node 436 and thus the feedback signal received at terminal407 is a positive voltage with respect to node 434 and terminal 405 ofthe integrated control circuit 401. Furthermore, in the illustratedembodiment of FIG. 4, sense circuit 414 provides a feedback signal atfeedback terminal 407 which is representative of output current I_(O)427 during the OFF state of switch 402.

FIG. 5 is a diagram illustrating a main inductor 500, in accordance withan embodiment of the invention. Main inductor 500 is one possibleimplementation of the first and second windings included in powerconverters 100, 200, 300 or 400 of FIGS. 1A, 1B, 2B, 2C, 3A, 3B, and 4.Main inductor 500 is illustrated in FIG. 5 as including a first winding504, a second winding 506 and a core 508. First winding 504 isillustrated as including a first wire 510, a terminal A 512 and aterminal B 514. The second winding 506 is illustrated as including asecond wire 516, a terminal C 518 and a terminal D 520.

As shown in FIG. 5, first winding 504 is magnetically coupled to secondwinding 506 by way of core 508. That is, core 508 is common to bothfirst winding 404 and to second winding 506. In one embodiment, firstwinding 504 and second winding 506 are first and second portions,respectively, of a main inductor. Thus, main inductor 500 may include awire wound around a single core where the wire has been separated intofirst wire 510 and second wire 516 corresponding to first winding 504and second winding 506, respectively. Although FIG. 5 illustrates core508 as a cylindrical rod, core 508 may be configured to include anysuitable shape, such as, an I-shaped core, a C- or U-shaped core, anE-shaped core, or an toroidal-shaped core, etc. In one embodiment, core508 includes a ferromagnetic material. In another embodiment core 508 isan air core, where wires 510 and 516 are stiff coil wire shaped to forma hollow space in the center of the coil.

The power supplies illustrated in FIGS. 6A, 6B, 7, 8 and 9 may beutilized in applications in which the load utilizes a negative voltagewhile the controller receives a positive voltage for the feedbacksignal. The power converters in FIGS. 6A, 6B, 7, 8, and 9 in generalhave inputs coupled to sources of electrical energy and have outputscoupled to a load. For example, power converter 600 includes terminals601 and 603 as an input coupled to a source of electrical energy (i.e.,source of input voltage V_(IN) 624). Power converter 600 also includesterminal 605 and 607 as an output that is coupled to load 638.

FIG. 6A is a schematic diagram illustrating a power converter 600 havinga switch S1 602 in an ON state, in accordance with an embodiment of thepresent invention. Power converter 600 is illustrated as includingswitch S1 602, a first winding 604, a second winding 606, a core 608, anoutput capacitor C_(O) 610, a diode D1 612, a controller 616, a commonreference 618, a resistor R1 644, and a resistor R2 646. Resistor R1 644and resistor R2 646 may also be referred to as a sense circuit. Firstwinding 604 is illustrated as including terminals C and D, while secondwinding 606 is illustrated as including terminals A and B. Switch S1 602is illustrated as including terminals 620 and 622. Also shown in FIG. 6Ais an input voltage V_(IN) 624, an output voltage V_(O) 626, a currentI_(ON) 628, a drive signal 632, a reference node 634, and a load 638.

As shown in FIG. 6A, first winding 604 is magnetically coupled to secondwinding 606 by way of core 608. That is, core 608 is common to bothfirst winding 604 and to second winding 606. In one embodiment, firstwinding 604 and second winding 606 are first and second portions,respectively, of a main inductor. Thus, a main inductor included inpower converter 600 may include a wire wound around a single core, wherethe wire has been separated into first and second portions correspondingto first winding 604 and second winding 606, respectively. In oneembodiment, core 608 includes a ferromagnetic material. Main inductor500 shown in FIG. 5 is one possible implementation of first winding 604and second winding 606.

In one example of the illustrated embodiment of power converter 600, thenumber of turns for first winding 604 is much greater than the number ofturns for second winding 606. When the number of turns for the firstwinding 604 is much greater than the number of turns for the secondwinding 606, output capacitor C_(O) 610 discharges during the ON timeand charges during the OFF time of switch S1 602. The output voltageV_(O) 626 may also be negative with respect to the common reference 618due in part to the duty ratio of drive signal 632.

Terminal D of first winding 604 is illustrated as being coupled toreceive input voltage V_(IN) 624. In one embodiment, power converter 600is an ac-dc power converter where input voltage V_(IN) 624 is a dcvoltage that has been generated by rectifying and filtering an ac inputvoltage. Power converter 600 may optionally include rectifier and filtercircuits (not shown) coupled to provide input voltage V_(IN) 624 toterminal D of first winding 604.

Switch S1 602 is illustrated as being coupled between first winding 604and second winding 606. More particularly, FIG. 6A illustrates terminal620 of switch S1 602 as being coupled to terminal C of first winding604, while terminal 622 of switch S1 602 is coupled to terminal B ofsecond winding 606. In one embodiment, switch S1 602 is coupled suchthat current I_(ON) 628 flows through first winding 604, through switchS1 602 and to output circuitry of the power converter 600 and to load638 when switch S1 602 is in an ON state (i.e., closed). In oneembodiment, output circuitry of the power converter 600 includes outputcapacitor C_(O) 610 through which at least a portion (i.e., currentI_(C)) of the current I_(ON) 628 can flow since the impedance of acapacitor, such as output capacitor Co 610, is very low. As illustratedin FIG. 6A, the current of the output capacitor Co 610 is illustrated ascurrent I_(C). In one embodiment it will be noted that the currentI_(ON) 628 that flows during the ON time of switch S1 602, flows in adirection that decreases the value of an output voltage Vo 626 acrossoutput capacitor Co 610. Switch S1 602 may be implemented as asemiconductor device such as for example a metal oxide semiconductorfield effect transistor (MOSFET), a bipolar junction transistor (BJT),or an insulated gate bipolar transistor (IGBT).

Controller 616 is coupled to provide drive signal 632 to controlswitching of the switch S1 602 to regulate an output of power converter600. The regulated output is generally in the form of a regulatedvoltage (e.g., output voltage V_(o) 626), current, output power or somecombination thereof. In other words, the controller 616 regulates theflow of energy to the output of the power converter 600. Controller 616regulates the output by controlling switch S1 602 to turn on and off inresponse to the signal received at the feedback terminal FB. In theexample, the signal received at the feedback terminal FB isrepresentative of the output voltage V_(O) 626. In other examples, thesignal received at the feedback terminal FB could be representative ofan output current, output power or some combination thereof. Controller616 may be implemented as a monolithic integrated circuit, or withdiscrete electrical components or a combination of discrete andintegrated components. Controller 616 and switch S1 602 could form partof an integrated control circuit that is manufactured as either a hybridor a monolithic integrated circuit. The controller 616 and switch S1 602may be referred to as a control circuit.

FIG. 6A further illustrates output capacitor C_(O) 610 as coupled acrosssecond winding 606 and diode D1 612. More particularly, one end of theoutput capacitor C_(O) 610 is coupled to terminal B of second winding606. The other end of the output capacitor C_(O) 610 is coupled to thecommon reference 618. In the illustrated embodiment, the outputcapacitor C_(O) 610 filters the output of the power converter 600 toprovide a substantially constant output voltage V_(O) 626 to the load638. As shown, the output voltage V_(O) 626 is the voltage across outputcapacitor C_(O) 610. In one embodiment, the voltage at common reference618 is greater than the voltage at terminal B of the second winding 606.As such, the output voltage V_(O) 626 is negative with respect to thecommon reference 618.

Second winding 606 is illustrated in FIG. 6A as being coupled betweenswitch S1 602 and diode D1 612. More particularly, terminal B of secondwinding 606 is coupled to output capacitor C_(O) 610 while terminal A iscoupled to diode D1 612. Diode D1 612 is illustrated as being coupledbetween second winding 606 and common reference 618. More particularly,an anode of diode D1 612 may be coupled to terminal A of the secondwinding 606, while a cathode of diode D1 612 is coupled to commonreference 618 to provide a path for the current from the second winding606 when switch S1 602 is in the OFF state. For example, FIG. 6B is aschematic diagram illustrating power converter 600 of FIG. 6A whenswitch S1 602 in the OFF state. As shown in FIG. 6B, during operation,controller 616 switches switch S1 602 to the OFF state, therebysubstantially preventing current from flowing through first winding 604and through switch S1 602. However, as illustrated in FIG. 6B, a current(i.e., current I_(OFF) 640) flows through second winding 606, which issubstantially the same as the current that flows through diode D1 612when switch S1 602 is in the OFF state. The current I_(OFF) 640 alsoflows to output circuitry of power converter 600. Since capacitor Co 610is typically a low impedance, at least a portion (i.e., current I_(C))of the current I_(OFF) 640 flows through the capacitor Co 610. It shouldbe noted that the direction of current flow I_(OFF) 640 is such that itwill increase the output voltage V0 626 across output capacitor Co 610.The direction of the current flow in output capacitor Co 610 during theON state of switch 602 is therefore opposite to the direction of currentflow in output capacitor Co 610 during the OFF state of switch 602 whilecurrent I_(OFF) 640 is flowing.

Referring now to both FIGS. 6A and 6B, power converter 600 may alsoinclude resistors R1 644 and R2 646 as a sense circuit to provide afeedback signal to controller 616. The feedback signal may be a voltagesignal or a current signal. In one embodiment, the feedback signalprovided by resistors R1 644 and R2 646 is a voltage signal. ResistorsR1 644 and R2 646 form a resistor divider on the output voltage V_(O)626. The feedback terminal FB of controller 616 is coupled betweenresistor R1 644 and resistor R2 646. In one embodiment, the feedbacksignal is the voltage across resistor R1 644. As mentioned above, inanother embodiment it is recognized that the feedback signal could berepresentative of an output current flowing in the load 638 or anotherparameter. In general the controller 616 is therefore responsive to afeedback signal to regulate the flow of energy to an output of the powerconverter, regardless of the parameter being regulated (output current,output voltage, output power, etc). In one embodiment, the outputvoltage V_(O) 626 is negative with respect to the common reference 618and the voltage at the common reference 618 is greater than the voltageat terminal 622 of switch S1 602. As such the voltage received at thefeedback terminal FB of the controller 616 is a positive voltage. In oneembodiment the sense circuit is coupled to load 638. That is, resistorsR1 644 and R2 646 may be coupled to load 638 without isolation circuitrytherebetween. Resistor R1 644 is coupled to one end of load 638 whileresistor R2 646 is coupled to the other end of load 638.

As shown in FIGS. 6A and 6B, the resistor divider formed by resistors R1644 and R2 646 (sense circuit) is also coupled to terminal 622 of switchS1 602. In one embodiment, resistors R1 644 and R2 646 generate thefeedback signal in response to a voltage taken with respect to terminal622 of switch S1 602. In one example terminal 622 of switch S1 602 isconnected to a common terminal COM of controller 616 by way ofconnection 642 as the reference ground of the controller 616. In oneexample the reference ground (e.g., common terminal COM) of thecontroller 616 is the reference voltage level relative to which drivesignal 632 is generated and the feedback signal is sensed. In oneembodiment, terminal 622 of switch S1 602 may be utilized as the commonterminal COM of controller 616. For the power converter 600 illustratedin FIGS. 6A and 6B, the power converter 600 provides a negative outputvoltage V_(O) 626 with respect to the common reference 618 to the load638 while the controller 616 of the power converter 600 receives apositive voltage at the feedback terminal FB.

FIG. 7 is a schematic diagram illustrating a power converter 700 withmultiple outputs, in accordance with an embodiment of the invention.Power converter 700 is illustrated as including switch S1 702, a firstwinding 704, a second winding 706, a core 708, a first output capacitorC_(O1) 710, a diode D1 712, a controller 716, a common reference 718, aresistor R1 744, a resistor R2 746, a diode D2 750, and a second outputcapacitor C_(O2) 752. The combination of resistor R1 744 and resistor R2746 may also be referred to as a sense circuit. First winding 704 isillustrated as including terminals C and D, while second winding 706 isillustrated as including terminals A and B. Second winding 706 alsoincludes a winding tap 707. Switch S1 702 is illustrated as includingterminals 720 and 722. Also shown in FIG. 7 are an input voltage V_(IN)724, a first output voltage V_(O1) 726, a second output voltage V_(O2)754, a drive signal 732, a first load 738, and a second load 756. Thepower converter 700 is similar to the power converter 600 shown in FIGS.6A and 6B however, power converter 700 illustrates an embodiment of thepresent with multiple outputs. Although, FIG. 7 illustrates powerconverter 700 as including two outputs, it should be appreciated that apower converter in accordance with embodiments of the present inventionmay have any number of outputs.

FIG. 7 further illustrates diode 712 and first output capacitor C_(O1)710 coupled to the winding tap 707 of second winding 706 to provide thefirst output voltage V_(O1) 726 to the first load 738. FIG. 7 alsoillustrates diode D2 750 and second output capacitor C_(O2) 752 coupledto terminal B of second winding 706 to provide the second output voltageV_(O2) 754 to the second load 756.

As shown in FIG. 7, first winding 704 is magnetically coupled to secondwinding 706 by way of core 708. That is, core 708 is common to bothfirst winding 704 and to second winding 706. In one embodiment, firstwinding 704 and second winding 706 are first and second portions,respectively, of a main inductor. Thus, a main inductor included inpower converter 700 may include a wire wound around a single core, wherethe wire has been separated into first and second portions correspondingto first winding 704 and second winding 706, respectively. In oneembodiment, core 708 includes a ferromagnetic material. Second winding706 further includes a winding tap 707, illustrated as coupled to diodeD1 712. In one example, winding tap 707 is an intermediate connectionbetween terminals of a winding (e.g., between terminals A and B ofsecond winding 706). Main inductor 500 shown in FIG. 5 is one possibleimplementation of first winding 704 and second winding 706, where aconnection is added to winding 504 to serve as winding tap 707.

In one example of the illustrated embodiment of power converter 700, thenumber of turns for first winding 704 is much greater than the number ofturns for second winding 706. When the number of turns for the firstwinding 704 is much greater than the number of turns for the secondwinding 706, output capacitor C_(O1) 710 discharges during the ON timeand charges during the OFF time of switch S1 702. The first outputvoltageV_(O1) 726 and second output voltage V_(O2) 754 may also benegative with respect to the common reference 718 due in part to theduty ratio of drive signal 732.

Terminal D of first winding 704 is illustrated as being coupled toreceive input voltage V_(IN) 724. In one embodiment, power converter 700is an ac-dc power converter where input voltage V_(IN) 724 is a dcvoltage that has been generated by rectifying and filtering an ac inputvoltage. Switch S1 702 is illustrated as being coupled between firstwinding 704 and second winding 706. More particularly, FIG. 7illustrates terminal 720 of switch S1 702 as being coupled to terminal Cof first winding 704, while terminal 722 of switch S1 702 is coupled tothe winding tap 707 of second winding 706 through diode D1 712. In oneembodiment, switch S1 702 is coupled such that current flows throughfirst winding 704, through switch S1 702 and to first output circuitryof the power converter 700 and to load 738 when switch S1 702 is in anON state (i.e., closed). In one embodiment, first output circuitry ofthe power converter 700 includes first output capacitor C_(O1) 710.Switch S1 702 may be implemented as a semiconductor device such as forexample a metal oxide semiconductor field effect transistor (MOSFET), abipolar junction transistor (BJT), or an insulated gate bipolartransistor (IGBT).

Controller 716 is coupled to provide drive signal 732 to controlswitching of the switch S1 702 to regulate an output of power converter700. The regulated output is generally in the form of a regulatedvoltage (e.g., first output voltage V_(O1) 726, second output voltageV_(O2) 754, or both), current, output power or some combination thereof.For the example illustrated, the power converter 700 regulates the firstoutput voltage V_(O1) 726. Controller 716 regulates the output bycontrolling switch S1 702 to turn on and off in response to the signalreceived at the feedback terminal FB. In the example shown in FIG. 7,the signal received at the feedback terminal FB is representative of thefirst output voltage V_(O1) 726. In other examples the signal receivedat the feedback terminal FB could be representative of an outputcurrent, output power or some combination thereof. Controller 716 may beimplemented as a monolithic integrated circuit, or with discreteelectrical components or a combination of discrete and integratedcomponents. Controller 716 and switch S1 702 could form part of anintegrated control circuit that is manufactured as either a hybrid or amonolithic integrated circuit. Controller 716 and switch S1 702 may bereferred to as a control circuit.

As mentioned above, power converter 700 has multiple outputs. In oneexample, one end of first output capacitor C_(O1) 710 is coupled todiode D1 712 and terminal 722 of switch S1 702 while the other end offirst output capacitor C_(O1) 710 is coupled to the common reference 718and terminal A of second winding 706. In the illustrated embodiment, thefirst output capacitor C_(O1) 710 filters one output of the powerconverter 700 to provide a substantially constant first output voltageV_(O1) 726 to the first load 738. As shown, the first output voltageV_(O1) 726 is the voltage across the first output capacitor C_(O1) 710.In one embodiment, the voltage at the common reference 718 is greaterthan the voltage at terminal 722 of switch S1 702. As such, the firstoutput voltage V_(O1) 726 is negative with respect to the commonreference 718.

In the illustrated example, one end of second output capacitor C_(O2)752 is coupled to diode D2 750 while the other end of second outputcapacitor C_(O2) 752 is coupled to the common reference 718 and terminalA of second winding 706. In the illustrated embodiment, the secondoutput capacitor C_(O2) 752 filters another output of the powerconverter 700 to provide a substantially constant second output voltageV_(O2) 754 to the second load 756. As shown, the second output voltageV_(O2) 754 is the voltage across the second output capacitor C_(O2) 752.In one embodiment, the second output voltage V_(O2) 754 is negative withrespect to the common reference 718. The magnitude of the second outputvoltage V_(O2) 754 may be greater than the magnitude of the first outputvoltage V_(O1) 726.

Second winding 706 is illustrated in FIG. 7 as being coupled betweendiode D2 750 and common reference 718. More particularly, terminal B ofsecond winding 706 is coupled to the cathode of diode D2 750 whileterminal A is coupled to common reference 718. The anode of diode D2 750is coupled to second output capacitor C_(O2) 752. In addition, thewinding tap 707 of second winding 706 is coupled to the cathode of diodeD1 712. The anode of diode D1 712 is coupled to first output capacitorC_(O1) 710. When switch S1 702 is in the OFF state, current flows fromthe second winding 706 to the output circuitry of power converter 700.For example, current flows from the second winding 706 to the outputcircuitry of second output capacitor C_(O2) 752 and second load 756.Current also flows from the second winding 706 to the output circuitryof the first output capacitor C_(O1) 710 and first load 738.

Resistors R1 744 and R2 746 form a sense circuit to provide a feedbacksignal to controller 716. The feedback signal received at the feedbackterminal FB of controller 716 may be a voltage signal or a currentsignal. In one embodiment, the feedback signal provided by resistors R1744 and R2 746 is a voltage signal. As illustrated, resistors R1 744 andR2 746 form a resistor divider on the first output voltage V_(O1) 726.The feedback terminal FB of controller 716 is coupled between resistorR1 744 and resistor R2 746. The voltage received at the feedbackterminal FB of controller 716 is substantially the voltage acrossresistor R1 744. As mentioned above, the first output voltage V_(O1) 726is negative with respect to common reference 718. As such, the voltagereceived at the feedback terminal FB of the controller 716 is positive.Resistor R1 744 is coupled to one end of the first load 738 whileresistor R2 746 is coupled to the other end of the first load 738. Inaddition, resistors R1 744 and R2 746 may be coupled to first load 738without isolation circuitry therebetween.

As shown in FIG. 7, the resistor divider formed by resistors R1 744 andR2 746 (sense circuit) is also coupled to terminal 722 of switch S1 702.In one embodiment, resistors R1 744 and R2 746 generate the feedbacksignal in response to a voltage taken with respect to terminal 722 ofswitch S1 702. In one example, terminal 722 of switch S1 702 isconnected to a common terminal COM of controller 716 by way ofconnection 742 as the reference ground of the controller 716. In oneexample the reference ground (e.g., common terminal COM) of thecontroller 716 is the reference voltage level relative to which drivesignal 732 is generated and the feedback signal is sensed. In oneembodiment, terminal 722 of switch S1 702 may be utilized as the commonterminal COM of controller 716. For the power converter 700 illustratedin FIG. 7, the power converter 700 provides a negative first outputvoltage V_(O1) 726 and a negative second output voltage V_(O2) 754 withrespect to the common reference 718 while the controller 716 of thepower converter 700 receives a positive voltage at the feedback terminalFB.

FIG. 8 is a schematic diagram illustrating a power converter 800 withmultiple outputs, in accordance with an embodiment of the invention.Power converter 800 is illustrated as including switch S1 802, a firstwinding 804, a second winding 806, a core 808, a first output capacitorC_(O1) 810, a diode D1 812, a controller 816, a common reference 818, aresistor R1 844, a resistor R2 846, a diode D2 850, and a second outputcapacitor C_(O2) 852. The combination of resistor R1 844 and resistor R2846 may also be referred to as a sense circuit. First winding 804 isillustrated as including terminals C and D, while second winding 806 isillustrated as including terminals A and B. Second winding 806 alsoincludes a winding tap 807. Switch S1 802 is illustrated as includingterminals 820 and 822. Also shown in FIG. 8 is an input voltage V_(IN)824, a first output voltage V_(O1) 826, a second output voltage V_(O2)854, a drive signal 832, a reference node 834, a first load 838, and asecond load 856. The power converter 800 is similar to the powerconverter 700 shown in FIG. 7 however, power converter 800 illustratesan embodiment of the present invention where a feedback voltage isgenerated in response to the second output (i.e., voltage across secondoutput capacitor C_(O2) 852). Although FIG. 8 illustrates powerconverter 800 as including two outputs, it should be appreciated that apower converter in accordance with embodiments of the present inventionmay have any number of outputs.

FIG. 8 further illustrates diode 812 and first output capacitor C_(O1)810 coupled to the winding tap 807 of second winding 806 to provide thefirst output voltage V_(O1) 826 to the first load 838. FIG. 8 alsoillustrates diode D2 850 and second output capacitor C_(O2) 852 coupledto terminal B of second winding 806 to provide the second output voltageV_(O2) 854 to the second load 856.

As shown in FIG. 8, first winding 804 is magnetically coupled to secondwinding 806 by way of core 808. That is, core 808 is common to bothfirst winding 804 and to second winding 806. In one embodiment, firstwinding 804 and second winding 806 are first and second portions,respectively, of a main inductor. Thus, a main inductor included inpower converter 800 may include a wire wound around a single core, wherethe wire has been separated into first and second portions correspondingto first winding 804 and second winding 806, respectively. In oneembodiment, core 808 includes a ferromagnetic material. Second winding806 further includes a winding tap 807, illustrated as coupled to diodeD1 812. In one example, winding tap 807 is an intermediate connectionbetween terminals of a winding (e.g., between terminals A and B ofsecond winding 806). Main inductor 500 shown in FIG. 5 is one possibleimplementation of first winding 804 and second winding 806, where aconnection is added to winding 504 to serve as winding tap 807.

In one example of the illustrated embodiment of power converter 800, thenumber of turns for first winding 804 is much greater than the number ofturns for second winding 806. When the number of turns for the firstwinding 804 is much greater than the number of turns for the secondwinding 806, output capacitor C_(O2) 852 discharges during the ON timeand charges during the OFF time of switch S1 802. The first outputvoltage V_(O1) 826 and second output voltage V_(O2) 854 may also benegative with respect to the common reference 818 due in part to theduty ratio of drive signal 832.

Terminal D of first winding 804 is illustrated as being coupled toreceive input voltage V_(IN) 824. In one embodiment, power converter 800is an ac-dc power converter where input voltage V_(IN) 824 is a dcvoltage that has been generated by rectifying and filtering an ac inputvoltage. Switch S1 802 is illustrated as being coupled between firstwinding 804 and second winding 806. More particularly, FIG. 8illustrates terminal 820 of switch S1 802 as being coupled to terminal Cof first winding 804, while terminal 822 of switch S1 802 is coupled toterminal B of second winding 806 through diode D2 850. In oneembodiment, switch S1 802 is coupled such that current flows throughfirst winding 804, through switch S1 802 and to the second outputcircuitry of the power converter 800 and to load 856 when switch S1 802is in an ON state (i.e., closed). In one embodiment, the second outputcircuitry of the power converter 800 includes second output capacitorC_(O2) 852. Switch S1 802 may be implemented as a semiconductor devicesuch as for example a metal oxide semiconductor field effect transistor(MOSFET), a bipolar junction transistor (BJT), or an insulated gatebipolar transistor (IGBT).

Controller 816 is coupled to provide drive signal 832 to controlswitching of the switch S1 802 to regulate an output of power converter800. The regulated output is generally in the form of a regulatedvoltage (e.g., first output voltage V_(O1) 826, second output voltageV_(O2) 854, or both), current, output power or some combination thereof.For the example illustrated, the power converter 800 regulates thesecond output voltage V_(O2) 854. Controller 816 regulates the output bycontrolling switch S1 802 to turn on and off in response to the signalreceived at the feedback terminal FB. In the example shown in FIG. 8,the signal received at the feedback terminal FB is representative of thesecond output voltage V_(O2) 854. In other examples the signal receivedat the feedback terminal FB could be representative of an outputcurrent, output power or some combination thereof. Controller 816 may beimplemented as a monolithic integrated circuit, or with discreteelectrical components or a combination of discrete and integratedcomponents. Controller 816 and switch S1 802 could form part of anintegrated control circuit that is manufactured as either a hybrid or amonolithic integrated circuit. Controller 816 and switch S1 802 may bereferred to as a control circuit.

As mentioned above, power converter 800 has multiple outputs. In oneexample, one end of first output capacitor C_(O1) 810 is coupled todiode D1 812 while the other end of output capacitor C_(O1) 810 iscoupled to the common reference 818. In the illustrated embodiment, thefirst output capacitor C_(O1) 810 filters one output of the powerconverter 800 to provide a substantially constant first output voltageV_(O1) 826 to the first load 838. As shown, the first output voltageV_(O1) 826 is the voltage across the first output capacitor C_(O1) 810.In one embodiment, the first output voltage V_(O1) 826 is negative withrespect to the common reference 818.

In the illustrated example, one end of second output capacitor C_(O2)852 is coupled to diode D2 850 and to terminal 822 of switch S1 802,while the other end of second output capacitor C_(O2) 852 is coupled tothe common reference 818. In the illustrated embodiment, the secondoutput capacitor C_(O2) 852 filters another output of the powerconverter 800 to provide a substantially constant second output voltageV_(O2) 854 to the second load 856. As shown, the second output voltageV_(O2) 854 is the voltage across the second output capacitor C_(O2) 852.In one embodiment, the voltage at the common reference 818 is greaterthan the voltage at terminal 822 of switch S1 802. As such, the secondoutput voltage V_(O2) 854 is negative with respect to the commonreference 818. The magnitude of the second output voltage V_(O2) 854 maybe greater than the magnitude of the first output voltage V_(O1) 826.

Second winding 806 is illustrated in FIG. 8 as being coupled betweendiode D2 850 and common reference 818. More particularly, terminal B ofsecond winding 806 is coupled to the cathode of diode D2 850 whileterminal A is coupled to common reference 818. The anode of diode D2 850is coupled to second output capacitor C_(O2) 852 and terminal 822 ofswitch S1 802. In addition, the winding tap 807 of second winding 806 iscoupled to the cathode of diode D1 812. The anode of diode D1 812 iscoupled to first output capacitor C_(O1) 810. When switch S1 802 is inthe OFF state, current flows from the second winding 806 to the outputcircuitry of power converter 800. For example, current flows from thesecond winding 806 to the output circuitry of second output capacitorC_(O2) 852 and second load 856. Current also flows from the secondwinding 806 to the output circuitry of the first output capacitor C_(O1)810 and first load 838.

The combination of resistors R1 844 and R2 846 form a sense circuit toprovide a feedback signal to controller 816. The feedback signalreceived at the feedback terminal FB of controller 816 may be a voltagesignal or a current signal. In one embodiment, the feedback signalprovided by resistors R1 844 and R2 846 is a voltage signal. Asillustrated, resistors R1 844 and R2 846 form a resistor divider on thesecond output voltage V_(O2) 854. The feedback terminal FB of controller816 is coupled between resistor R1 844 and resistor R2 846. The voltagereceived at the feedback terminal FB of controller 816 is substantiallythe voltage across resistor R1 844. As mentioned above, the secondoutput voltage V_(O2) 854 is negative with respect to common reference818. As such, the voltage received at the feedback terminal FB of thecontroller 816 is positive. Resistor R1 844 is coupled to one end of thesecond load 856 while resistor R2 846 is coupled to the other end of thesecond load 856. In addition, resistors R1 844 and R2 846 may be coupledto load 856 without isolation circuitry therebetween.

As shown in FIG. 8, the resistor divider formed by resistors R1 844 andR2 846 (sense circuit) is also coupled to terminal 822 of switch S1 802.In one embodiment, resistors R1 844 and R2 846 generate the feedbacksignal in response to a voltage taken with respect to terminal 822 ofswitch S1 802. In one example, terminal 822 of switch S1 802 isconnected to a common terminal COM of controller 816 by way ofconnection 842 as the reference ground of the controller 816. In oneexample the reference ground (e.g., common terminal COM) of thecontroller 816 is the reference voltage level relative to which drivesignal 832 is generated and the feedback signal is sensed. In oneembodiment, terminal 822 of switch S1 802 may be utilized as the commonterminal COM of controller 816. For the power converter 800 illustratedin FIG. 8, the power converter 800 provides a negative first outputvoltage V_(O1) 826 and a negative second output voltage V_(O2) 854 withrespect to the common reference 818 while the controller 816 of thepower converter 800 receives a positive voltage at the feedback terminalFB.

FIG. 9 is a schematic diagram illustrating power converter 900 withmultiple outputs, in accordance with an embodiment of the invention.Power converter 900 is illustrated as including switch S1 802, firstwinding 804, second winding 806, core 808, a first output capacitorC_(O1) 910, a diode D1 912, controller 816, a common reference 918, aresistor R1 944, a resistor R2 946, a diode D2 950, and a second outputcapacitor C_(O2) 952. The combination of resistor R1 944 and resistor R2946 may also be referred to as a sense circuit. First winding 804 isillustrated as including terminals C and D, while second winding 806 isillustrated as including terminals A and B. Second winding 806 alsoincludes a winding tap 807. Switch S1 802 is illustrated as includingterminals 820 and 822. Also shown in FIG. 9 is input voltage V_(IN) 824,a first output voltage V_(O1) 926, a second output voltage V_(O2) 954,drive signal 832, reference node 834, a first load 938, and a secondload 956. The power converter 900 is similar to the power convertersillustrated in FIGS. 7 and 8, however, power converter 900 illustratesan embodiment of the present invention where one output voltage isnegative with respect to the common reference 918 and the other outputvoltage is positive with respect to the common reference 918. AlthoughFIG. 9 illustrates power converter 900 as including two outputs, itshould be appreciated that a power converter in accordance withembodiments of the present invention may have any number of outputs.

Input voltage V_(IN) 824, switch S1 802, first winding 804, secondwinding 806, core 808, controller 816, and drive signal 832 couple andfunction with respect to each other as described above. FIG. 9 alsoillustrates the common reference 918 as coupled to the winding tap 807of second winding 806. In addition, FIG. 9 further illustrates diode D1912 and first output capacitor C_(O1) 910 coupled to terminal B ofsecond winding 806 to provide the first output voltage V_(O1) 926 to thefirst load 938. FIG. 9 further illustrates diode D2 950 and secondoutput capacitor C_(O2) 952 coupled to terminal A of second winding 806to provide the second output voltage V_(O2) 954 to the second load 956.As illustrated first output capacitor C_(O1) 910 and second outputcapacitor C_(O2) 952 couple to the winding tap 807 and common reference918.

In one example of power converter 900, the number of turns for firstwinding 804 is much greater than the number of turns for second winding806. When the number of turns for the first winding 804 is much greaterthan the number of turns for the second winding 806, first outputcapacitor C_(O1) 910 discharges during the ON time and charges duringthe OFF time of switch S1 802. The first output voltage V_(O1) 926 mayalso be negative with respect to the common reference 918 due in part tothe duty ratio of drive signal 832.

As mentioned above, switch S1 802 is illustrated as being coupledbetween first winding 804 and second winding 806. More particularly,FIG. 9 illustrates terminal 820 of switch S1 802 as being coupled toterminal C of first winding 804, while terminal 822 of switch S1 802 iscoupled to terminal B of second winding 806 through diode D1 912. In oneembodiment, switch S1 802 is coupled such that current flows throughfirst winding 804, through switch S1 802 and to the first outputcircuitry of the power converter 900 and to load 938 when switch S1 802is in an ON state (i.e., closed). In one embodiment, the first outputcircuitry of the power converter 900 includes first output capacitorC_(O1) 910.

Controller 816 is coupled to provide drive signal 832 to controlswitching of the switch S1 802 to regulate an output of power converter900. For the example illustrated, the power converter 900 regulates thefirst output voltage V_(O1) 926. Controller 816 regulates the output bycontrolling switch S1 802 to turn on and off in response to the signalreceived at the feedback terminal FB. In the example shown in FIG. 9,the signal received at the feedback terminal FB is representative of thefirst output voltage V_(O1) 926.

Power converter 900 has multiple outputs. In one example, one end offirst output capacitor C_(O1) 910 is coupled to diode D1 912 and toterminal 822 of switch S1 802, while the other end of output capacitorC_(O1) 910 is coupled to the common reference 918 and the winding tap807 of second winding 806. In the illustrated embodiment, the firstoutput capacitor C_(O1) 910 filters one output of the power converter900 to provide a substantially constant first output voltage V_(O1) 926to the first load 938. As shown, the first output voltage V_(O1) 926 isthe voltage across the first output capacitor C_(O1) 910. In oneembodiment, the voltage at the common reference 918 is greater than thevoltage at terminal 822 of switch S1 802. As such, the first outputvoltage V_(O1) 926 is negative with respect to the common reference 918.

In the illustrated example, one end of second output capacitor C_(O2)952 is coupled to diode D2 950, while the other end of second outputcapacitor C_(O2) 852 is coupled to the common reference 918 and windingtap 807 of second winding 806. In the illustrated embodiment, the secondoutput capacitor C_(O2) 952 filters another output of the powerconverter 900 to provide a substantially constant second output voltageV_(O2) 954 to the second load 956. As shown, the second output voltageV_(O2) 954 is the voltage across the second output capacitor C_(O2) 952.In one embodiment, the second output voltage V_(O2) 954 is positive withrespect to the common reference 918.

Second winding 806 is illustrated in FIG. 9 as being coupled betweendiode D1 912 and diode D2 950. More particularly, terminal B of secondwinding 806 is coupled to the cathode of diode D1 912 while terminal Ais coupled to the anode of diode D2 950. The anode of diode D1 912 iscoupled to first output capacitor C_(O1) 910 and terminal 822 of switchS1 802. In addition, the winding tap 807 of second winding 806 iscoupled to the common reference 918. The cathode of diode D2 950 iscoupled to second output capacitor C_(O2) 952. When switch S1 802 is inthe OFF state, current flows from the second winding 806 to the outputcircuitry of power converter 900. For example, current flows from thesecond winding 806 through diode D2 950 and to the output circuitry ofsecond output capacitor C_(O2) 952 and second load 956. Current alsoflows from the winding tap 807 of the second winding 806 to the outputcircuitry of the first output capacitor C_(O1) 910 and first load 938.

The combination of resistors R1 944 and R2 946 form a sense circuit toprovide a feedback signal to controller 816. The feedback signalreceived at the feedback terminal FB of controller 816 may be a voltagesignal or a current signal. In one embodiment, the feedback signalprovided by resistors R1 944 and R2 946 is a voltage signal. Asillustrated, resistors R1 944 and R2 946 form a resistor divider on thefirst output voltage V_(O1) 926. The feedback terminal FB of controller816 is coupled between resistor R1 944 and resistor R2 946. The voltagereceived at the feedback terminal FB of controller 816 is substantiallythe voltage across resistor R1 944. As mentioned above, the first outputvoltage V_(O1) 926 is negative with respect to common reference 918. Assuch, the voltage received at the feedback terminal FB of the controller816 is positive. Resistor R1 944 is coupled to one end of the first load938 while resistor R2 946 is coupled to the other end of the first load938.

As shown in FIG. 9, the resistor divider formed by resistors R1 944 andR2 946 (sense circuit) is also coupled to terminal 822 of switch S1 802.In one embodiment, resistors R1 944 and R2 946 generate the feedbacksignal in response to a voltage taken with respect to terminal 822 ofswitch S1 802. In one example, terminal 822 of switch S1 802 isconnected to a common terminal COM of controller 816 by way ofconnection 842 as the reference ground of the controller 816. In oneexample the reference ground (e.g., common terminal COM) of thecontroller 816 is the reference voltage level relative to which drivesignal 832 is generated and the feedback signal is sensed. In oneembodiment, terminal 822 of switch S1 802 may be utilized as the commonterminal COM of controller 816. For the power converter 900 illustratedin FIG. 9, the power converter 900 provides a negative first outputvoltage V_(O1) 926 and a positive second output voltage V_(O2) 954 withrespect to the common reference 918 while the controller 816 of thepower converter 900 receives a positive voltage at the feedback terminalFB.

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific embodimentsdisclosed in the specification. Rather, the scope of the invention is tobe determined entirely by the following claims, which are to beconstrued in accordance with established doctrines of claiminterpretation.

1. A power converter, comprising: a first winding; a second windingmagnetically coupled to the first winding; a switch coupled between thefirst winding and the second winding; a controller having a feedbackterminal and a common terminal, wherein the controller is coupled tocontrol the switch to regulate an output of the power converter inresponse to a feedback voltage received at the feedback terminal andwherein the feedback voltage is a positive voltage with respect to thecommon terminal; and an output circuit coupled between the commonterminal of the controller and a common reference of the power converterto provide an output voltage to a load, wherein the output voltage is anegative voltage with respect to the common reference of the powerconverter.
 2. The power of claim 1, wherein the common terminal of thecontroller is coupled to a terminal of the switch.
 3. The powerconverter of claim 1, wherein the output circuit includes an outputcapacitor having one terminal coupled to the common terminal of thecontroller and another terminal coupled to the common reference of thepower converter.
 4. The power converter of claim 3, further comprising adiode coupled between the second winding and the common reference of thepower converter such that a current flows through the second winding andthe diode when the switch is in an OFF state.
 5. The power converter ofclaim 1, further comprising a main inductor, wherein the first windingis a first portion of the main inductor and wherein the second windingis a second portion of the main inductor.
 6. The power converter ofclaim 5, wherein the main inductor comprises a ferromagnetic core andwherein the first portion of the main inductor includes a first wirewound around the ferromagnetic core and wherein the second portion ofthe main inductor includes a second wire wound around the ferromagneticcore.
 7. The power converter of claim 1, further comprising a sensecircuit coupled to the feedback terminal of the controller, wherein thesense circuit generates the feedback voltage in response to the outputvoltage.
 8. The power converter of claim 7, wherein sense circuitincludes a resistor divider coupled to receive the output voltage. 9.The power converter of claim 1, wherein the output circuit is a firstoutput circuit coupled to provide a first output voltage to a firstload, wherein the first output voltage is a negative voltage withrespect to the common reference of the power converter, the powerconverter further comprising a second output circuit coupled to thesecond winding and the common reference of the power converter toprovide a second output voltage to a second load.
 10. The powerconverter of claim 9, wherein the second output voltage is a negativevoltage with respect to the common reference of the power converter. 11.The power converter of claim 9, wherein the second output voltage is apositive voltage with respect to the common reference of the powerconverter.
 12. The power converter of claim 1, wherein the secondwinding includes a tap element, and wherein the switch is coupled,through a diode, to the tap element of the second winding.
 13. The powerconverter of claim 1, wherein the controller is coupled to control theswitch to regulate the output voltage of the power converter in responseto the feedback voltage received at the feedback terminal.
 14. A powerconverter, comprising: a first winding; a second winding magneticallycoupled to the first winding; and a control circuit coupled between thefirst and second windings, wherein the control circuit includes: a firstterminal coupled to the first winding; a second terminal coupled to thesecond winding; a switch coupled between the first terminal and thesecond terminal of the control circuit; a feedback terminal coupled toreceive a feedback voltage, wherein the feedback voltage is a positivevoltage with respect to the second terminal of the integrated controlcircuit; and a controller coupled to control the switch to regulate anoutput voltage of the power converter in response to the feedbackvoltage, wherein the output voltage is a negative voltage with respectto a common reference of the power converter.
 15. The power converter ofclaim 14, further comprising an output capacitor having one terminalcoupled to the second terminal of the integrated control circuit andanother terminal coupled to the common reference of the power converter.16. The power converter of claim 15, further comprising a diode coupledbetween the second winding and the common reference of the powerconverter such that a current flows through the second winding and thediode when the switch is in an OFF state.
 17. The power converter ofclaim 14, further comprising a main inductor, wherein the first windingis a first portion of the main inductor and wherein the second windingis a second portion of the main inductor.
 18. The power converter ofclaim 17, wherein the main inductor comprises a ferromagnetic core andwherein the first portion of the main inductor includes a first wirewound around the ferromagnetic core and wherein the second portion ofthe main inductor includes a second wire wound around the ferromagneticcore.
 19. The power converter of claim 14, further comprising a sensecircuit coupled to the feedback terminal of the controller, wherein thesense circuit generates the feedback voltage in response to the outputvoltage.
 20. The power converter of claim 19, wherein sense circuitincludes a resistor divider coupled to receive the output voltage. 21.The power converter of claim 14, wherein the output circuit is a firstoutput circuit coupled to provide a first output voltage to a firstload, the power converter further comprising a second output circuitcoupled between the second winding and the common reference of the powerconverter to provide a second output voltage to a second load, whereinthe second output voltage is a negative voltage with respect to thecommon reference of the power converter.
 22. The power converter ofclaim 14, wherein the second winding includes a tap element, and whereinthe switch is coupled, through a diode, to the tap element of the secondwinding.
 23. The power converter of claim 14, wherein the controller iscoupled to control the switch to regulate the output voltage of thepower converter in response to the feedback voltage received at thefeedback terminal.
 24. The power converter of claim 14, wherein theswitch is a metal oxide field effect transistor (MOSFET) having a drainterminal coupled to the first terminal and a source terminal coupled tothe second terminal of the integrated control circuit.
 25. A powerconverter, comprising: an input to be coupled to a source of electricalenergy; an output to be coupled to a load; a capacitor coupled acrossthe output; a first winding coupled to the input; a second windingmagnetically coupled to the first winding; and a control circuit coupledbetween the first and second windings, wherein the control circuitincludes: a first terminal coupled to the first winding; a secondterminal coupled to the second winding; a switch coupled between thefirst terminal and the second terminal of the control circuit, wherein afirst current flows through the first winding and the switch when theswitch is in an ON state, wherein at least a portion of the firstcurrent flows in the capacitor in a first direction; a feedback terminalcoupled to receive a feedback signal, wherein the control circuit iscoupled to control the switch to regulate a flow of energy to the outputof the power converter in response to the feedback signal; wherein asecond current flows through the second winding during a time when theswitch is in an OFF state, wherein at least a portion of the secondcurrent flows in the capacitor in a second direction and wherein thesecond direction is opposite the first direction of the portion of thefirst current.
 26. The power converter of claim 25, wherein thecapacitor has one terminal coupled to the second terminal of the controlcircuit and another terminal coupled to a common reference of the powerconverter.
 27. The power converter of claim 25, further comprising amain inductor, wherein the first winding is a first portion of the maininductor and wherein the second winding is a second portion of the maininductor.
 28. The power converter of claim 27, wherein the main inductorcomprises a ferromagnetic core and wherein the first portion of the maininductor includes a first wire wound around the ferromagnetic core andwherein the second portion of the main inductor includes a second wirewound around the ferromagnetic core.
 29. The power converter of claim25, further comprising a sense circuit coupled to the feedback terminalof the controller, wherein the sense circuit generates the feedbacksignal
 30. The power converter of claim 29, wherein sense circuitincludes a resistor divider coupled to receive an output voltage. 31.The power converter of claim 25, wherein the switch is a metal oxidefield effect transistor (MOSFET) having a drain terminal coupled to thefirst terminal and a source terminal coupled to the second terminal ofthe integrated control circuit.